Nitinol Is A Material We Need To Be Playing With More

Nitinol tire

Another Kickstarter, another opportunity for people to get mad at delayed and poorly functioning (if delivered at all) gadgets. This project aims to make airless tires for bikes and scooters using nitinol, and despite the company’s failed attempt at pedaling their wares on Shark Tank last year, the campaign has already more than quadrupled its funding goal.

The real star of the show here is NiTinol, a shape metal alloy composed of nickel and titanium. We should soon see a real commercial application of this miracle metal, and not long after we’ll see what happens when the rubber meets the road on these airless tires and their long-term performance. It’s not accurate to say they don’t use rubber; they just use LESS, because they’re still treaded, albeit with a layer that is adhered to the metal coil, and you don’t need tubes, either. The tread will still wear down and needs to be replaced occasionally for the lifetime of the tire, but the real advantage is never having a flat tire again. Considering how inconvenient flats are and the number of meetings I’ve been late commuting to because of an unplanned rapid deflation, these tires might be worth it. If you’re wondering why they’re so expensive, some napkin calculations of the nitinol coil have somewhere between 100 ft – 200 ft of wire per wheel, and at $1-2/ft, the raw materials alone before assembly make it an expensive piece of kit.

So what’s so cool about nitinol that it’s worth playing with, and what does it do that spring steel or stainless steel can’t? Well, you can soak it in acid for a year, and it will continue unaffected. It has excellent bio-compatibility, so you can put it in someone’s arteries as a stent, and it will go through tens of millions of cycles without cracking. It’s 10 times better at recovery and lighter, and it’s not magnetic, which can be useful. The memory capability is handy, too, because it means you can rapidly prototype springs, then heat and quench them to set their memory and easily adjust them.

Admittedly, I don’t have a use for it right now. But just like the coils of nichrome and piano wire waiting anxiously in my bins for their opportunity to shine, nitinol is screaming for a fun use.

51 thoughts on “Nitinol Is A Material We Need To Be Playing With More

  1. I did a Master’s thesis in SMA actuators using NiTi back in 2003, it is a fun material but fairly hard to make a reliable, repeatable, fast moving device with it, and also hard to actuate it electrically, because maintaining a good electrical contact is tough, while insulating the part. The use of it as a basic spring in a tyre – seems overkill – it’s not cheap, even now.

      1. Regarding liquid SiO2, that stuff actually is everywhere these days. Every modern automobile/aviation ceramic coating/polish is using it. It’s pretty much on most of the phones out there that have hydrophobic/oleophobic screens. Fabrics are treated with it to repel stains; you can even buy it yourself from Amazon to spray on your own fabrics.

      2. Imma be completely honest, this is my first time here about these. It just popped up in my news feed and thought “different”. This is also my first time hearing about liquid glass and that article is from 2010 lol.
        I’m kinda shocked I’ve never heard of either of them given I’m a contractor and I work on bikes as a hobby, Trek, Huffy, Schwinns, DK, Mongoose, Diamondback, BMX bikes, Mountain bikes speed bikes, I enjoy working on all of them.. Clearly they haven’t done anything to make real headlines. But they do need to figure something out with the price of the material to make it. They wanna talk about it being better for the earth but very few people will be able to afford them or would be willing to spend that kinda money.

        1. Well in fairness there isn’t much point in having a refurbishing line for a pile of tyre that are not yet even in existence, and several hundred? thousand? miles or many years probably from wearing out…

          Not quite sold on this idea myself, I’ve had flats before, who hasn’t… But good tyre and tube seems to be very much sufficient. That said I’m not sure if I should be envious of you for having bike lanes that are apparently useful, or sad that they are apparently intentionally used for broken glass storage… Which would put even a good tyre to the test with regular exposure.

      1. I have Dutch Perfect tires, which have a thick rubber layer with embedded kevlar. Since I started using those, rarely have a flat. Rolling resistance is said to be higher, but I don’t notice the difference.

      2. Every city bike lane would be a storage place for glass and pieces of metal if it wasn’t that every day sweeper cars clean them. Don’t you have those?

        The advantage for these tires in my view comes from now e-bikes taking over, and those enable everybody to go on long ditance trips, and having a flat in the middle of nowhere is rather annoying so if you can avoid that at least it’s a worry less.

    1. I believe this is what is called inability to use spellcheck, which is endemic on hackaday.

      Of course you can always write your articles in rhyming slang and claim any mistakes are intentional, but they will be unreadable to the parts of your audience who are not native speakers, and probably also to all those who are, but don’t come from the same district of London as you.

        1. Springs don’t snap from fatigue unless they’re regularly overloaded, though. So long as the load is kept below the fatigue limit, a steel spring should never fail. Using nitinol for this seems like meme tech.

          1. Yes. However, the reversible plastic strain for nitinol is about 8-10% whereas for steel it’s about 0.5% so it’s much harder to reach the endurance limit. You have much more margin for deformation that is still reversible.

          2. There’s also some interesting features to the stress-strain curve of nitinol where it goes flat, which is the point where normal metals would yield permanently, but nitinol just springs back. In that region, nitinol acts like a spring of constant force regardless of displacement.

    1. I’m guessing that the nitinol spring is compacted or compressed so that it can be fitted inside the tire. After the tire is mounted on its rim you heat the spring by passing electrical current through it to cause it to expand an fill the tire cavity. This expansion presses against the tire tread from the inside to provide enough force to support the weight of the rider.

  2. Too expensive for me. I’d like to try it, but I won’t purchase it. It’s 469 euro’s, but after it goes through customs I have to pay a total of 664 euro’s, for one pair of tires. For 100 euro’s I have two Continental GP5000’s on my roadbike. For 150 I have a spare one. I’ve once changed a tire in under 2 minutes (track bike, front tire, on someone elses bicycle, right before a race). I get the appeal, I love the tech behind it, but for me, it makes no sense to actually purchase it for these prices. I rarely have flats and a tiny kit with an inner tube (yeah I still ride clinchers), CO2 pump and steel reinforced tire levers are cheap, simple and it’s a quick job for me. I’m not planning on driving through acid (although I clean my tires with vinegar before riding on the velodrome). And these tires still wear. Maybe less, but they still wear out. I love the technology behind it, don’t get me wrong. But I don’t see the value in them.

    1. I’m unconvinced that tubeless for road bikes is a good idea. It’s been great on my xc and dh bikes but my coworkers, except for the one rocking the Zipp 808’s, have all had issues with standard rims converted to or new-built for tubeless. It seems to need slightly wider rims and less than 5 bar pressure or it just leaks down to 5 bar and then gets super squirmy in turns on bikes whose rims aren’t purpose built for lower pressure tires.

  3. A solution looking for a problem. A bike tire(and tube) can be replaced or repaired in minutes, especially enough to get you to where you are going. Seconds if you use the temporary “Fix-A-Flat” products. Those are available in bicycle-sized “doses”. The only solution to repairing this overpriced product is to send it off to the retread facility, pay for that, pay for shipping, possibly pay VAT’s and Customs fees(both ways), and wait for months for all of that to happen.

    No, thank you.

  4. Orthodontists use nitinol wire in traditional braces (brackets glued to teeth, etc.). What most people don’t know about orthodontics is that the small spring force provided by that tiny wire attached to the brackets is what moves the teeth.

    Your teeth normally find a position where the forces applied by your lips/cheeks/tongue/occlusion are all balanced. Orthodontists put a piece of nitinol wire on brackets to alter that balance which causes the teeth to shift in usually predictable ways. As the tiny force is applied by the wire to the teeth, bone is resorbed in the direction of motion and reformed on the opposite side. If you try to move the teeth too quickly, the reform part of the process can’t keep up and you end up with loose teeth. That is why you have to wear braces for such a long time. It’s also why you need a retainer after the braces are taken off. If you don’t use a retainer, your teeth are going to try to move back where they were.

    If you or your kid has braces, the orthodontist periodically changes out the nitinol wire. They normally throw it away. Tell them you’d like to have it and they’ll give it to you. It’s fun to play with!

    1. “What most people don’t know about orthodontics is that the small spring force provided by that tiny wire attached to the brackets is what moves the teeth.”

      Who doesn’t know that? I mean… people are ignorant, but there’s nothing else that COULD be doing it. The interesting tidbit here is that the wire is often nitinol.

  5. I could see it being interesting if it could be integrated into a metal structure so that it could act like an actuator. Unfortunately, the cost of energy (and there for utilizing) titanium (a fantastic metal) is going to keep this from being a reality for the foreseeable future.

  6. It does have a number of neat uses, even before the biocompatible stuff.

    I’ve got a short wire whip antenna made of the stuff; it’s great for not taking permanent kinks and for being pretty stiff for its weight. It’s coated in some stretchy insulation, which works fine, so some electric heating seems reasonably possible.

    All the ones that are made for superelasticity have to be used in a 40-50C range above their transition temperature for the effect to work. When you approach the cold end of the temperature range, the wires become much less springy – it’s much worse than with air, and you can’t just inflate the tires more in the winter to make up for it – you have to keep them warm somehow. This range may or may not be the same as the range your tire has to experience – not that I’d like to ride a bike on ice in the winter, but if you choose the transition temperature so that it will be superelastic in icy slush, then you will probably find that it loses superelasticity when you are on hot asphalt in the summer. You could probably do fine if you use wires of two different transition temperatures together, but now you’ve increased costs again.

    The cool diy-friendly stuff to me might be things like the nitinol motors and actuators, especially ones that are specifically made to act on changes in temperature automatically without power consumption. E.G. a greenhouse that can open its own vents.

    1. “E.G. a greenhouse that can open its own vents.”

      there’s a clever, and (unfortunately) cheaper way to do that which is already in common use – you can buy pistons which use the thermal expansion of a gas or wax mixture in the piston to open vents as they heat up. In the case of wax, the liquid phase of the wax only has 5-20% greater volume than the solid phase, but it can be used to generate impressive force through hydraulic pressure (this how the thermostats on nearly all liquid-cooled engines work, as well as most thermostatic mixing valves)

      nitinol actuators are very cool – for small-scale applications they have one of the highest power-to-weight and power-to-size ratios you can get in any form, and they’re amazingly simple – but for the big stuff, there tend to be much more affordable options.

      1. I do know about those, and you’re right that it’s a cheap way to do it – but I was under the impression the lower temperature bound was significantly higher than you can get with nitinol, in addition to the short stroke / high force needing to be transformed. Do you know of any that actuate around 5-15 deg C for instance? If so, I’d guess it might act a bit like a snap disc (having a bit of a lag & hysteresis) except it’d be an actuator instead of closing contacts. (Lower-temperature snap discs can be useful for heating systems whose purpose is just to protect against water freezing, so that’s why they’re on my radar)

  7. These tires, and all other airless tires, lack the ability to adjust pressure for different riding situations and rider weights. That’s a big step backwards in tuning the feel of a bicycle. If they were very cheap and directed at commuter riders where the ability to fine tune ride quality with small pressure changes isnt so important maybe that would be a good use case. As it is you can buy a VERY flat resistant tire coupled with some type of sealant(in tubes or a tubeless set up) and flats will be almost non-existent. A set up like that would cost a consumer abt $80-$100/wheel including installation labor.

      1. Pretty much all amateur
        but serious (and a lot of not so serious) mountainbikers here in Chile use normal, not flat resistant tyres with sealant. In a country full of thorns and a damned thorny tree (google “espinos”), it is a smart solution. If you get a hole so big sealant won’t work, you actually -find- a thorn and stick it in the hole… and let the liquid do the magic. Due to the cheaper labor, its half of what they said above, or similar if you use really high end tyres.

  8. Opinionated Dutch rider and maintainer of bikes here. This concept is terrible on just about every level. From what I can see, this system is not compatible with normal rims. What I see on the video is that the “tire” is acting like a semi-deflated tube, which means more resistance and rim damage, even if the tire is not damaged which I doubt when hitting a curb or stone at speed. and the idea of those replaceable strips for grip sounds like a fine sales-model, but nothing more.

    Look, good inner and outer tubes are a fraction of the cost of this solution to a problem that does not exist. Even then, mending a tire is not rocket science. If you want to cycle, learn how to do that and you are golden.

  9. So I’m supposed to boil my wheels every time I hit some discontinuity on the street? I stay out of bike lanes cause of the trash, I like cars and trucks, they help crush and pick up glass and nails. Retreads? Now another hazard in the bike lane to avoid. The amount of retread scraps on state roads is going up. I can’t tell if is it’s a dead coon or tire toppings.

    1. The primary property of NiTinol in use here is the fact that it can be bent far more than most metals and not get permanently deformed – to put it another way “no, it’ll just spring back into shape”.

  10. It should be noted that back in 2017, NASA made an entire rover wheel out of NiTinol to try to increase durability in harsh environments.

    And they literally did the same thing in the 60’s for the wheels on the Apollo Rover with piano wire, which proved to be fantastic under lunar conditions.

  11. I agree with most of the posts: great material but wrong application. Recreational cyclers need to learn to fix flats. It’s part of the sport. Commuters who don’t care to fix their flats should carry a Slime-type product to get their bike to a repair shop. The potential medical applications are pretty cool, though.

  12. The was a Veritasium video on NASA’s exploration of using NiTinol for wheels and it does a good job of explaining why it might make sense for NASA (I can’t seem to post a link to the video though).

    But like many of the commentors here I’m very skeptical of this product. There are lots of red flags to justify that skepticism. It’s trying to ride on NASA’s name and reputation, it’s trying to commercialize an idea that hasn’t been field-tested by NASA, it’s trying to get funding via routes like Kickstarter and Shark Tank, and the company is more marketing than substance.

  13. I spent 5 years as.the product manager at Raychem for Cryofit Marine couplings. It’s seductive stuff but usually ends up being the most expensive substitute for bolts, nuts, clamps etc.

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